Is recommending aspirin next?

Should aspirin be recommended to prevent cancer? Many lines of evidence have suggested that regular low-dose aspirin reduces the risk of colorectal cancer. Can the inexpensive wonder drug reduce the risk of other cancers as well? Researchers in England led by Dr. Peter Rothwell recently published three meta-analyses that looked at aspirin use and long-term cancer incidence and metastasis, as well as the short-term effect on cancer incidence and mortality, and the effect of aspirin on cancer metastasis. More than 200 studies were included in the meta-analyses, which were initially done to assess aspirin's benefit on vascular disease. The three new studies used a combination of case-control, cohort, and randomized clinical trials.

In the long-term study, the 20-year risk of cancer death and metastases was evaluated whereas the short-term study looked at a 3-5 year time frame. The trial for prevention of metastatic disease included five large, randomized trials of daily aspirin vs control in patients who had new solid cancer diagnosed during the trial. In the long-term study, the odds ratio for colon cancer incidence was 0.62 in favor of aspirin, and the odds ratio was 0.58 for death from colon cancer in favor of aspirin. There were similar reductions in the rates of esophageal, gastric, biliary, and breast cancer. The rate of distant metastases was also reduced. The other two studies also showed reduced rates of cancer and reduced rates of metastatic disease.

In the short-term study, cancer rates were 24% lower with aspirin use at 3 years. Curiously, aspirin did not reduce the risk of vascular events but there was no increased risk of major bleeding, including intracranial hemorrhage.

In the meta-analysis of five trials looking at the rate of metastatic disease, a 36% reduction in cancer metastasis was noted, including a 46% reduction in metastatic adenocarcinoma (all three studies published online in Lancet and Lancet Oncology March 21, 2012.) An accompanying editorial points out that these studies show that aspirin at any dose reduces nonvascular deaths by 12% and cancer death by 15% with benefits seen within 3 years for higher doses (> 300 mg/day) and at 5 years for lower doses (< 300 mg/day). The major critique of the studies comes from the United States where the Women's Health Initiative Study and the Physicians' Health Study both failed to show benefit from aspirin on cancer mortality. Both of these studies used low-dose aspirin every other day, a dose that may be too low to show biological effect on cancer. Another critique suggests that aspirin may lead to earlier diagnosis of colorectal cancer since it may cause earlier gastrointestinal bleeding, explaining the lower mortality rate. Despite these concerns, the editorialists suggest that this "impressive collection of data moves us another step closer to broadening recommendations for aspirin use. Moreover, future evidence-based guidelines for aspirin prophylaxis can no longer consider the use of aspirin for the prevention of vascular disease in isolation from cancer prevention." (Lancet published online March 21, 2012).